Operating methods and control devices of this type are used especially in modern Diesel and Otto engines, for example, in order to directly move a valve needle of the fuel injector back and forth between different working positions and thereby control the injection of fuel. The use of piezoelectric actuators is advantageous in this context in particular in view of the high dynamic demands in connection with the movement of the valve needle.
However, the mechanical and electrical characteristics of the utilized piezoelectric actuators do not remain constant throughout their service life. Both an actuator travel and the rigidity as well as the electrical capacity of the piezoelectric actuator change over the course of the service life. A direct detection of these changes during operation, and thus their compensation as well, is impossible without complicated measuring technology. This results in errors in the injected fuel quantity.
Wear of possibly installed additional components, especially hydraulic components, that are part of a chain of action which includes the valve needle and the piezoelectric actuator, may also have a negative effect on the precision of the injected fuel quantity.